The predicted structure of dystrophin, the protein known to be altered in Becker and Duchenne muscular dystrophy, indicates that dystrophin interacts with other proteins in muscle cells. The objectives of this grant are to determine what proteins interact with dystrophin, how and why they bind to dystrophin, and the identity of these dystrophin associated of dystrophin in normal muscle cells. The nature of the associated binding proteins and the resulting dystrophin-associated protein complex is key to understanding the importance of the dystrophin complex to muscle. This work has enormous consequences as to how the Duchenne and Becker phenotypes arise at the molecular and clinical levels. Other dystrophies such as limb-girdle (LGD) and fascioscapulahumeral (FSH) resemble the Becker phenotype. As such, it is possible that some portion of the dystrophin complex is altered in these other dystrophies. Therefore, the study of dystrophin binding proteins may uncover the defect in other, related dystrophies. In general terms, this work is of fundamental value in many areas of basic and clinical neurobiology.